(a) Field of the Invention
The present invention pertains to terrain analysis and, more particularly, to a method for rapidly determining visibility features of broad geographic regions.
(b) Description of Related Art
There are numerous applications for a system capable of rapidly characterizing the visibility features of broad geographic regions. Rapid characterization of the visibility features of a geographic area lends itself to many military applications. For example, a military commander would be able to query a terrain characterization system to find all regions which have east visibility and north concealment. A terrain characterization system would generate a map that illustrates such areas for the commander. Using such a map would allow the positioning of military reconnaissance forces to the west of an enemy camp while avoiding visual exposure to military forces to the north.
One civilian application of a terrain characterization system is that of determining placements for wireless and/or cellular base stations. In many cases, the line-of-sight visibility from a transmitting tower to a service area must be determined. The determination of line-of-sight visibility between two points is relatively simple, and can be done by analyzing a digital elevation map. A digital elevation map is a topographical map on which a grid is overlaid. Each cell of the grid contains a number representative of the elevation of that cell. To have line of sight visibility between two points, the area between the two points must not go above a straight line extended between the points. Although the actual task of determining area coverage (i.e., how much of an area is visible and how much of an area is concealed) once a proposed base station location has been chosen is generally rather simple, the task of actually choosing a particular base station location is very time consuming when using this trial and error basis.
It is possible to determine the regions visible from a single point through the use of a ray trace fan. A typical ray trace involves first reading an elevation value at a given grid square on a digital elevation map. From that grid square, in each direction, any point below the level of a ray from the grid square is marked as being non-visible. If the elevation value of a point is above the level of the ray, the point is marked as being visible and the angle of the ray is increased to match the elevation of the point. This method allows for the calculation of visible and concealed areas from the chosen point. By repeating this process using each grid square as a starting point, the visibility of an entire region may be determined.
The magnitude of calculations that must be made to determine the visibility of each point in all directions using ray trace procedures can be readily appreciated. Known terrain analysis systems perform all necessary calculations each time the system is used or a query is requested. This creates large computation overhead and, accordingly, a need for large computational power. Therefore, it would be desirable to perform computer terrain analysis of visible and concealed regions in a rapid and computationally efficient manner. Additionally, it would be desirable to provide a terrain analysis system capable of responding to queries regarding various visibility and concealment criteria in a compact unit.